Tests on an 84-month-old Holstein showed the cow, born at a ranch on Japan's northernmost island of Hokkaido, was infected with the fatal illness, it said. The animal will be destroyed and incinerated so its parts will not be circulated for consumption or used as feed, the ministry said on its website.

Japan has now confirmed 31 animals infected with the illness - known formally as bovine spongiform encephalopathy, or BSE - since the country's first case was detected in 2001.

The degenerative nerve disease found in older cattle has been linked to the rare but fatal human variant Creutzfeldt-Jakob disease.

Japan banned American beef in December 2003 after the first reported case of mad cow disease in a U.S. herd. Tokyo eased the ban in July after U.S. and Japanese officials hammered out a deal that included strict requirements and stringent checks at U.S. meat processing plants.